The present invention relates to a scanning method and apparatus and particularly to a method and apparatus for scanning documents and providing an accurate electrical representation of such documents without requiring exact mechanical alignment of the scanning mechanism.
In document scanners, either of the "pushbroom" type wherein a photosensitive array is moved relative to a document or the rotating drum type wherein the document is moved with respect to a photosensitive array, mechanical misalignment or imperfection in the mechanical movement can cause a skewed or distorted electrical output.
Typically, a line of pixels oriented in the X axis direction is imaged on a linear photosensitive array such as a charge coupled device, while the charge coupled device is scanned mechanically in the Y axis direction, either by movement of the device or by movement of the document being scanned. This motion provides a swath of pixels perpendicular to the X axis. If the mechanical scan mechanism, for example a "y-arm", is not perfectly straight and perpendicular to the X axis, scanning inaccuracy will result. For instance, a "vertical" line in the Y direction will appear wavy or crooked if reproduced from the electrical output.
Of course, this problem could be solved by providing a nearly perfect mechanical scan mechanism and nearly perfect alignment between the scanning apparatus and the document being scanned. However, such a solution is often impractical and expensive.